This invention relates to a method for curing certain resin precursors, and to novel thermosetting resin precursor compositions, such being useful to provide an ink suitable for solventless printing.
In many instances condensation reactions associated with the curing of certain condensate resin precursors require elevated temperatures to proceed at a suitable reaction rate. It is common, therefore, to employ a strong acid such as para-toluenesulfonic acid as a catalyst in these instances. Such an acid, however, catalyzes the condensation reaction to a significant extent even at room temperature and is unsuitable for applications wherein the promotion of the condensation reaction at room temperature cannot be tolerated.
This invention is of particular importance in the curing of amino resins, alkyd resins, modified alkyd resins (for example, those which have been modified by the incorporation of a drying oil, a vinyl monomer, a urea, a melamine or the like), and especially in the cross-linking of alkyd resins with an amino resin precursor.
Many resin precursors can be cured either by lengthy exposure to high temperature or under less severe conditions by the addition of a strong acid catalyst immediately prior to curing. The acid catalysts used heretofore in the art, however, must not be added to resin precursors which are intended to be stored because they promote the hardening or gellation of the compositions at a finite rate even at room temperature. The shelf stability of resin precursors containing such catalysts is very short, the compositions becoming unworkable after only a few hours of storage.
It is apparent that the addition of a strong acid catalyst, para-toluenesulfonic acid for example, to the resin precursor immediately prior to curing obviates the storage problem and reduces the severity of the conditions needed to cure the composition but this alternative suffers from the added cost and complications associated with a separate and additional processing step.
There is, therefore, a need for a condensate resin precursor composition having good shelf stability which will rapidly cure without the addition of a separate catalyst.
There further remains a need for a method for curing a condensate resin precursor which operates only at temperatures above typical storage temperatures (e.g. 20-40.degree. C.) and which does not require the addition of a catalyst immediately prior to curing.